Fog inhibitor for photographic emulsions



Patented Jan. 4, 1949 roe INHIBITOR FOR PHOTOGRAPHIC. EMULSIONS RobertEliot Staufler and William F. Smith,

Rochester, N. Y., assignors to Eastman Kodak Company, Rochester N. Y..,.a corporation of New Jersey No Drawing. Application October 17, 1947, Serial No. 780,568

12 Claims. (Cl. 95-7) This invention relates to fog-inhibiting agents and stabilizers for photographic emulsions and to photographic emulsions containing them.

It is known that photographic emulsions, particularly ultra-sensitive emulsions or those .containing optical sensitizers exhibit. a tendency to form a .depositof silver in the emulsion. This deposit extends more .or less .uniformlyover the entire emulsion and is known .as fog. Photographic fog is of two types: local and general. Local fog is formed by exposure of the film or plate at undesired points as by a light leak in the camera. General tag is formed in a number of ways. It may be caused by the conditions under which the film or plate is stored such as conditions of high temperature or-humidity or unusually long time of storage. The nature of the emulsion may also produce general fogas well as the conditions of development of the emulsion as by development for protracted periods of time or'at temperatures above normal. We are primarilyconcernedwith the fogand sensitivity changes in films .or plates which have been stored under adverse conditions of temperature and humidity.

General fog and loss of sensitivity of the emulsion are especially likely to occur-When the sensitive material is stored under conditions other than ideal, that is, underconditions of high temperature and humidity as in'tropical reg-ions.

It is an object of the invention to provide novel anti-fogging or fog-inhibiting compounds for emulsions. A further object is to provide anti: fogging agents which stabilize..the initial sensitivity oi the emulsion. AstiIlQfurther object is to provide anti-fogging agents which improve the keeping of the emulsion in tropical regions. Other objects will appear from the following description of our invention.

These objects are accomplished by incorporating in a silver halide emulsion an acid orasalt having the general formula:

RzReXs in which R is hydrogen, ammonium or an alkali metal. X is a halogen atom, and ,Re is the :element rhenium. p v,

Compounds suitable for use according;to.;our invention are, those. of the above general .iormula, in which R; is hydrogen, ammonium or an-alkali metal such as sodium or potassium and X is a halogen atom such as chlorine, bromine or iodine. Suitable compounds are potassium chlororhenate, KzReCls; potassium bromo. rhenate,.K2ReBrs and potassium iodorhenate, KzReIs.

Theobject of our invention is to maintain the sensitivity and fog of silver halide emulsions .at or close :to initial optimum values under keepin conditions of high temperature and humidity. Thetfoginhibitors which we vpropose to use are added to the emulsion during the processoi manufacture to avoid loss of sensitivity. andto inhibit-the growth of fog with passage of time under non-ideal conditions of storage.

Asolution of RzRXs compound when added in suitable. concentration before coating to unsensitized. or optically sensitized photographic emulsions does not appreciably affect the sensitometric-values for sensitivity and fog when measurements are made soon after coating. When sensitometric' measurements, are made at apprecl-ableintervals ofltime under tropical or dry conditions of storage at elevated temperatures. however," this compound does stabilize photo graphic speed andmaintain fog at a low level. The preparation of silver halideemulsions-in: volves three separate operations (1) the emulsification and digestion or ripening ofpthe silver halide, (2) the freeing of thezemulsion from excess soluble salts usuallyby washing, l3) the second digestion or after-ripening to obtain in: creasedsensisivity. (ll/lees, The Theory of'the Photographic.Process,,. '942.) We p fer tor-add the fog-inhibiting agents after. the final digestion or after-ripening although they may be addedbefore digestion; The most :v useful concentration range of.;fog inhibitor is -from .26 ,to 3.9 gm. of fo inhibitor per kilogram of silver nitrate .used in making the particular-silver, halide emulsion and converted to silver: halide. willof course vary for example depending on the silver halideor-mixture of halides used.

The antifoggant and'stabilizing action was determined by incubation of the emulsions under simulated tropical conditions and also by incubation. at lowrelative humidity at 12091 for various lengths of time from. 1,2 daystoonemonth. The results of these vtests are-tabulated heregand are comnaredswlth the-initial speed, ammaandiog of the emulsions: withand, without ,1 the t The quantity used foggant and stabilizing compound. The tests from which the following tabulation was made used a high-speed silver bromoiodide emulsion exposed on an Eastman type IIB sensitometer and developed for five minutes in a developer of the following composition:

tiguous to the silver halide emulsion. In these cases we use the same or a slightly greater ratio of rare metal salt to silver halide as when the salt is in the emulsion layer.

It will be understood that we contemplate as included within our invention all modifications and equivalents falling within the scope of Grams the appended claims. Monomethyl paraminophenol sulfate 2.5 What We claim sodmm Fiulfite (deslccated) 10 1. A silver halide emulsion layer containing a Hydroqumone compound having the structure Sodium metaborate 10. RZReXG Potassium bromide 0.5 v water to one liter. where X is a halogen atom and R is of the group consisting of hydrogen, ammonium and alkali The results for KzReCls are as follows: metals Gms. of compound Original 12 Days at 120 F. 1 Mo. Tropical lKg. AgNO; (converted to AgX) used in emulsion l0/i speed Gamma Fog l0/i speed Gamma Fog l0/i speed Gamma Fog None 455 1.41 .20 455 1.44 .25 202 1.56 .20 465 1.31 .20 540 1.31 .26 200 1. 51 .21 .52 425 1.40 .14 615 1.30 .20 255 1.43 .13 1.3 345 1.46 .14 .18 162 1.63 .14

One of the advantages of our invention is the fact that compounds such as KZReCIs are readily prepared with high purity. KzReCls is prepared and may be used as follows:

The compound was prepared by intimately mixing powdered potassium chloride and rhenium metal, and fusing carefully at dull red heat in a silica tube and silica combustion boat in a current of dry chlorine gas. The temperature was not allowed to go too high in order to prevent sublimation of rhenic chloride from the tube. After cooling in a chlorine atmosphere, the greenish yellow sintered mass was dissolved in water, filtered to remove unreacted metal and carefully crystallized by concentration at room temperature over sulfuric acid in a vacuum desiccator. The crystals of KzReCls were pale green showing a high index of refraction and high dispersion. They appear isomorphic with KzPtCls (potassium hexachloroplatinate). The rhenium complex was dissolved in water at a convenient concentration and was added to a melted gelatinosilver bromo-iodide photographic emulsion in quantities ranging up to about 3.9 grams per kg. of AgNO3 (converted to AgX) in the emulsion. The emulsion was coated on a suitable support, glass, film, or other, and was dried in the normal way. The other RzReXs compounds may be prepared and used in a similar manner.

Another and perhaps chief advantage is the greater extent of stabilizing action over a wide range of climatic conditions.

The fog inhibiting agents which we have described may be used in various kinds of photographic emulsions. In addition to being useful in ordinary non-sensitized emulsions they may also be used in orthochromatic, panchromatic and X-ray emulsions. If used with sensitizing dyes, they may be added to the emulsion before or after the dyes are added. Various silver salts may be used as the sensitive salt such as silver bromide, silver iodide, silver chloride and mixtures of these. The dispersing agents may be gelatin or other colloid such as collodion, albumen, cellulose organic derivatives or synthetic resins.

We also contemplate as a part of our invention those cases where it is desirable to coat the antifoggant in a colloid layer such as gelatin on either or both sides of or also in a silver halide emulsioniayer, so that the antifoggant is con- 2. A silver halide emulsion layer containing a compound having the structure RzReXe RzReCls where R is of the group consisting of hydrogen, ammonium and alkali metals.

4. A silver halide emulsion layer containing a compound having the structure RzReBrs where R is of the group consisting of hydrogen, ammonium and alkali metals.

5. A silver halide emulsion layer containing a compound having the structure RzReIs where R is of the group consisting of hydrogen, ammonium and alkali metals.

6. A silver halide emulsion layer containing a compound having the structure RzReCls where R is an alkali metal.

7. A silver halide emulsion layer containing a. compound having the structure RzReBro where R is an alkali metal.

8. A silver halide emulsion layer containing a compound having the structure RzReIa where R is an alkali metal.

9. A silver halide emulsion containing potas sium chlororhenate.

10. A silver halide emulsion containing potassium bromorhenate.

11. A silver halide emulsion containing potas-. sium iodorhenate.

5 6 12. A light sensitive photographic element comwhere X is a halogen atom and R is of the group prising a silver halide emulsion layer and a colconsisting of hydrogen, ammonium and alkali loid layer contiguous to said emulsion layer, at metals. least one of said layers containing a compound ROBERT ELIOT STAUFFER. having the structure 5 WILLIAM F. SMITH.

RzReXs No references cited. 

